refactor(loader): A3 — unificar loader, eliminar duplicación

El loader vivía partido: arje-brain/loader.rs cargaba EntityCards Y
Rules, mientras brahman-cards tenía su propia infra de card-loading.

Resolución por linaje:
- Card-loading (load_card_file, extract_card_from_json) → brahman-cards
  (entity_loader.rs). Toda card-loading del ecosistema vive ahí.
- Rule-loading (load_rules_file, extract_rules_from_json) → arje-brain-rules
  (loader.rs), junto a la definición de Rule.
- arje-brain/loader.rs eliminado.

arje-brain re-exporta ambos para compat de consumidores (arje-zero).
cargo check --workspace verde. Tests: 13 arje-brain-rules + 31 brahman-cards.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

crates/runtime/arje-brain-rules/src/lib.rs

@@ -7,7 +7,9 @@
 pub mod rules;
 pub mod engine;
 pub mod dispatch;
+pub mod loader;
 
 pub use rules::{Action, EventKind, EventPattern, LogLevel, Rule, Scope, TimedEvent};
 pub use engine::{EventKindDiscriminant, RuleEngine, SubjectInfo};
 pub use dispatch::{dispatch_actions, ActionSink, NullSink};
+pub use loader::{extract_rules_from_json, load_rules_file};